GF42.50-P-4001RIT Traction System Hydraulic Unit, Component Description

GF42.50-P-4001RIT Traction system hydraulic unit, component description

MODEL 230.479 with CODE (P99) Special model "AMG Black Series"

Component Identification:

Location
The traction system hydraulic unit is located in the right rear of the engine compartment and forms a unit together with the ESP, SPS [PML] and BAS control unit.

Task
The switching components of the following vehicle dynamics control systems are combined in the traction system hydraulic unit:

- Electronic Stability Program (ESP)
- Anti lock brake system (ABS)
- Acceleration skid control (ASR)
- Brake Assist (BAS)
- Electronic brake force distribution (EBD [EBV])

Design
The following components are integrated in the traction system hydraulic unit:

- Front axle prepressure sensor (A7/3b1)
- Left front pressure sensor (A7/3b3)
- Right front pressure sensor (A7/3b4)
- Left rear pressure sensor (A7/3b5)
- Right rear pressure sensor (A7/3b6)
- High pressure charge pump (A7/3m1)
- Front axle balance valve (A7/3y3)
- Rear axle balance valve (A7/3y4)
- Left front inlet control valve (A7/3y6)
- Left front outlet control valve (A7/3y7)
- Right front inlet control valve (A7/3y8)
- Right front outlet control valve (A7/3y9)
- Left rear inlet control valve (A7/3y10)
- Left rear outlet control valve (A7/3y11)
- Right rear inlet control valve (A7/3y12)
- Right rear outlet control valve (A7/3y13)
- Front axle switchover solenoid valve (A7/3y18)
- Rear axle switchover solenoid valve (A7/3y19)
- Front axle intake solenoid valve (A7/3y22)
- Rear axle intake solenoid valve (A7/3y23)
- Low pressure reservoir
- Damper

Function
The naturally aspirated high pressure charge pump integrated into the traction system hydraulic unit is pulse-actuated for pressure buildup and reduction for the ASR and ESP control interventions and for return flow in ABS control interventions.

The intake solenoid valves are opened during an ASR or ESP pressure buildup phase so that the brake fluid from the reservoir can be delivered via the high pressure charge pump to the respective wheel brake cylinder. The balance valves are analogized valves which can be set to a condition between open and closed. For pressure control, one 2/2 directional control valve (inlet control valve) is used for the functions of pressure buildup and pressure hold in ABS, ASR and ESP control mode. For limp-home, the inlet control valves are kept open when de-energized. This ensures that the driver can build up enough brake pressure in the system even if the ABS function fails. The outlet control valves serve to reduce brake pressure to counteract the blocking tendency in ABS control mode.

For pressure control, one 2/2 directional control valve (outlet control valve) is used for the functions of pressure hold and pressure reduction in ABS, ASR and ESP control mode. For limp-home, the outlet control valves are kept closed when de energized.

For ABS, ASR and ESP control interventions the switchover solenoid valves cut off front axle pressure circuit and the rear axle pressure circuit between the wheel brakes and the master brake cylinder. They are designed simultaneously as pressure limiting valves and open at a pressure of approx. p = 150 bar.

The brake fluid flowing away via the switchover solenoid valve is lead back to the master brake cylinder.

The low pressure reservoirs in the ABS, ASR or ESP sense the brake fluid during the pressure reduction phase and forward it to high-pressure charge pump.

Each brake circuit is equipped with its own damper to reduce delivery noise and to dampen a pulsating brake pedal.